interact with https://apiadv.sintia.com.ar/Help/Api/POST-Ratificacion-Login

func login(username, password string) (Token, error) {
  res, err := http.Post("https://apiadv.sintia.com.ar/api/Login",
    "application/json",
    strings.NewReader(fmt.Sprintf(`{"username": "%s", "password": "%s"}`, username, password)),
  )
  if err != nil {
    return "", err
  }
  defer res.Body.Close()
  if res.StatusCode != 200 {
    return "", errors.New("invalid username/password")
  }
  var t Token
  dec := json.NewDecoder(res.Body)
  if err := dec.Decode(&t); err != nil {
    return "", err
  }
  return t, nil
}